The manufacture of semiconductor devices involves creating a semiconductor wafer and performing various processing techniques on the wafer. One such technique includes performing lithography by exposing the wafer with a projected image that depends upon circuitry design to be embodied on the wafer. Before projecting the image, a photo-resist coating and an anti-reflective coating (ARC) are applied to the surface of the wafer. To ensure that the projected image is properly exposed onto the wafer, it is important that the photo-resist and ARC coatings be smooth and coat the wafer completely.
In order to effectively coat the wafer surface with photo-resist and ARC coatings, the surface of the wafer must be covered with a pre-wet solvent. This pre-wet solvent is dispensed onto the wafer prior to the photo-resist and ARC coatings being dispensed. The pre-wet solvent provides a smooth, wet surface for the photo-resist and ARC coatings to spread over and helps to break the surface tension of the photo-resist and ARC as it spreads.
However, problems have arisen with the use of this system of dispensing. While the photo-resist or ARC coatings are being dispensed, the semiconductor wafer spins at a relatively high spin speed. This high speed causes the pre-wet solution that has already reached the outer portions of the wafer to dry before the photo-resist or ARC reaches the outer portions. The dry surface prevents even coating by the photo-resist and ARC coatings and leads to manufacturing defects. To reduce these manufacturing defects, additional photo-resist or ARC has been used. However, these solutions are extremely expensive. In particular, the photo-resist can cost up to $10,000 per gallon.